This invention relates to moldable materials prepared by blending thermoplastic compositions to obtain multiple component blends which have a combination of advantageous characteristics. The conversion of plastics utilizes machinery adapted to fabricate the plastic at temperatures within a range which is significantly narrower than the range of softening points of the polymeric resins which scientists have produced. Moreover, impact resistance for blends is difficulty attainable, so that any blend having outstanding impact resistance has aroused the interest of industrial designers.
Polyurethane resin is an example of a polymer having sufficiently high impact resistance and sufficient elasticity to be employed as a thermoplastic rubber. It is not practical to employ such thermoplastic rubber in some conventional equipment for molding selected articles having restricted flexibility. However, blends comprising resins and rubbery materials can be molded to produce impact-resistant articles of interest to some fabricators.
Polystyrene is among the less costly of commercially used resins, but some types of polystyrene have blending characteristics making them unsuitable for fabrication of articles having high resistance to impact. Various proposals have been made for blends comprising polystyrene and appropriate rubbery components.
Lauchlan, et al, U.S. Pat. No. 3,660,531 describes the preparation of a resin blend containing polystyrene and significant amounts of an elastomer for imparting impact resistance.
Fava U.S. Pat. No. 4,129,619 describes a blend of polymethyl methacrylate and styrene-maleimide copolymer.
Fava U.S. Pat. No. 4,129,615 describes a blend of styrene-maleimide with an interpolymer of styrene, methyl methacrylate, and a rubbery component comprising 65-95% alkadiene and 5-35% vinyl aromatic component.
Most attempts to mix pellets of different molding compositions are unsatisfactory because of the general incompatibility of polymeric materials. When a mixture of molding pellets is extruded, there is generally a very weak extrudate by reason of the fracture lines at the boundaries amongst the different compositions. The discovery of a compatible blend of plastic, sometimes referred to as "plastic alloys", is a significant and unexpected discovery by reason of the incompatibility of most of the conceivable permutations of mixtures of plastics.
Nowithstanding the persistent effort to prepare appropriate blends, there has been a failure by others to prepare blends meeting some of the combinations of desired properties which are attained by the present invention.